from appropriate readings-or by traversing the saddle; and using a using end gauges against stops. On tool of reverse shape, a boss can be BY GEOMETER a lathe, however, it would mean machined if required, as at B. Hole loosening and resetting the work, a centres in plate material or castings longer and more difficult job. The may be located by marking off in the boring tool of the jig-borer must be ordinary way; then the scribed lines adjustable for sizing holes, and this can be set vertically and laterally to SED to its full extent with arrives from a form of radial feed to a needle point spinning truly in the accessory equipment, the the tool or its tip. chuck, as at C-the same as on a jig- U lathe is undoubtedly the Turning now to the lathe, the jig- borer-and noting the feedscrew read- most versatile of machine tools, boring principle is obtained, as at A, ings. For the lathe setting, a needle with a boring tool in the independent and all types with rotating spindles can be soldered into a piece of brass owe something to it. Certainly each may perform some particular ,E!?!P - operation or group of operations faster and with greater facility than the lathe,. as is the case with bench and pillar drills, milling A machines, and universal and surface 0 grinders. Various operations spec- ial to these machines can be per- formed reasonably efficiently on the lathe, given time, moderate dimensions in the work and some ingenuity in the set-up. The same is true to a considerable extent of the jig-borer, which operates in the reverse way to a lathe, working with a single-point boring tool-and with special emphasis on accuracy. For a normal boring operation on a lathe, the work revolves mounted in the chuck or on the faceplate, and the single-point boring tool is set to cut and feed. For the corresponding operation on a jig-borer, the work is stationary on the machine table, while the single-point boring tool revolves and is fed, The reason for this reversal is the nature of the work. In the main a jig consists of a built-up plate or cast box structure in which components can be placed, for drills, reamers, etc., to be applied to them through ac- curately positioned bushed holes- chuck and the work mounted on the rod. Having obtained the position thus speeding production by obviating vertical slide,, set to face the chuck of one hole (top left), the centre of marking off and numerous different and fixed, hke the crossilide, by another (bottom right) follows from settings for each component. In tightening the gib-piece screws. With- a lateral feed X and a vertical feed Y. constructing the jig, all holes (some out a special tool or holder, tool feed Holes may be centre drilled, drilled, of them perhaps not very large) must can be given by manipulating the then bored from the chuck. T be accurately placed and bored- chuck jaws, and testing results with a On a jig-borer, holes at right angles and it is easier to do this spinning a gauge or callipers in the bore.Positions and other angles require the work to boring tool than swinging a massive of different holes can be obtained be mounted on fixed and adjustable casting or a long piece of plate from cross-slide and vertical slide angle plates. This principle may material. screws when these have micrometer follow on the lathe, though some 1 The table of the jig-borer can be collars. Slides may have to be loosened settings can be obtamed by turning moved by accurate feed screws in two for moving; and while accuracy may the slide, as at D, much easier than directions at right angles; and having not compare with a jig-borer, it by the normal lathe principle. Radius picked up the position of a hole on should be equal to that from ordinary machining, too, may sometimes be the feed screw micrometer collars, marking off. simpler as at E, on a saddle casting, the positions of others can be obtained Ordinary cutting feed follows from if large. 11 DECEMBER 1958 739 MODEL ENGINEER
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